1. Field of the Invention
This invention relates to a method and an apparatus for generating an x-, a y-, and a z-coordinate signal for an x, y, z display device.
The term x, y, z display device shall include in particular and preferably x, y, z oscilloscopes of any type. However, this term shall also include all types of x, y, z printers which are suitable for signal recording in the x, y, z mode by means of an active element such as a stylus or printing jet, in particular ink jet printers.
The invention can be employed in any field in which test signals are obtained or measured and displayed on display devices. However, the preferred area of application for this invention is the field of electromedicine.
2. Description of the Prior Art
In the field of electromedicine, signals which give information about the patient's status are taken from a patient's body via electrodes or sensors in a variety of forms. Such body signals, called also physiological signals are, for instance, electrocardiogram (EKG) signals, blood pressure signals, respiratory signals, temperature signals, CO.sub.2 content signals indicating the carbon dioxide content in the blood or respiration gas of a patient. Such signals are normally displayed on a suitable display device, e.g., an oscilloscope or a recorder.
The display of measured signals such as body signals of a patient, on a display device such as an x, y, z display device presents no problems if for each measurement location, that is e.g. for each individual patient, a separate display device is used. This display device should operate entirely independently of display devices of other measurement locations, e.g., other patients.
A first problem arises, however, if display devices assigned to different measurement locations are to be coupled with a central station or with one another, so as to make it possible to transmit signal images of one display device to a central station or to another display device. This coupling should be performed at lowest possible cost and without distortion of the images.
Added to this first problem is a second problem. This occurs when in addition to test signals, which normally are present in analog form, also alphanumerical symbols such as numbers, letters or other symbols, are to be transmitted between and displayed by separate display devices or between display devices and a central station.
Heretofore, such signal mixtures of analog signals and alphanumerical character signals could, without too great an expense, be transmitted only within chains by means of video receivers. The image resolution of video receivers, however, is low. In particular, in the medical sector, it is not sufficient for the desired degree of image resolution of physiological signals. Character transmission is sometimes difficult.
A sufficiently good image resolution may be obtained with simple x, y, z display devices, in particular, with normal x, y, z oscilloscopes. Using these devices, analog signals and character signals have already been displayed jointly with a high degree of resolution. However, in the prior art both signals were only displayed on a single device. Coupling with other devices with the possibility of image transmission between all or some of these devices of the system at comparatively low cost has heretofore been impossible. Such instrumentation or system requires transmission of high frequency, wide bandwidth data. It was typically accomplished with multiple coaxial cables at considerable expense. In fact, as is known, unblanking pulses for the z-control of an x, y, z display device for the display of an alphanumerical character, have a very high frequency and a large bandwidth. To date, transmission of such characters between individual display devices at acceptably low cost and without distortion was hardly feasible because of the different frequency transit times resulting from the different delay times in the transmission paths between the various display devices.